David Robson: Some bugs like it hot

Japanese beetles didn't love the weather this summer, but we had other small visitors in our lawns and gardens.

David Robson

Gardening wouldn’t be interesting if there were no problems, especially six-legged types.

This year has been interesting for what we’ve seen, what we haven’t, and what is to be expected.

Think back to what the weather has been like the last six weeks. We haven’t experienced daytime temperatures below 80 degrees. Instead, we hit the 90s. And the temperature stayed there, causing us to sweat and power company officials to rub their hands with satisfaction.

When the thermometer started to climb, the copper and green Japanese beetles started to decline. (When something unwanted disappears, we tend not to shed any tears.) As the 90 degree-plus days piled up, the beetles rapidly bit the dust, which was better than biting the roses. Instead of staying around through July and into August feeding on lindens, roses, birches and Shasta daisy, the beetles were mostly gone by the last week of July.

Of course, they still did significant damage during their four to six weeks of feeding. And you will have to decide if you would rather have 90 degree-plus days or Japanese beetles.

Related to the Japanese beetles were the June beetles, or masked chafers. These creatures don’t do much feeding on plants, but like Japanese beetles, lay their eggs in turfgrass. In August, all these eggs from both beetles hatch and become the dreaded lawn grubs.

The female beetle can’t lay eggs in hot, dry, concrete-like soil. That’s Positive Point 1. However, if you water your lawn, you’ve created the perfect egg-laying environment.

Once the eggs hatch, if they aren’t fried by the hot, dry, concrete-like soil (Positive Point 2), the grubs are likely to die because of the hot, dry, concrete-like soil themselves. That’s Positive Point 3.

All is predicated on a turf that’s allowed to go dormant in the heat. If you water and water, you may have grubs.

While the beetles were falling by the wayside, another insect was making itself known this year: the magnolia scale. We’ve had magnolia scale in years past, but not as bad as this year. They just exploded.

Scales by nature are sap-sucking creatures, and in most cases, seldom cause the death of any plant outside. On indoor houseplants, however, their populations can build to the point where it’s just easier to throw the plant away than to wage a battle with the scales.

Outdoors, we often find scales on Wintercreeper Euonymus, pin oak trees, pine trees and a few other plants. In most cases, the creatures tend to be cyclic, rising and declining based on the weather and predatory insects such as ladybugs.

Plants are usually only hit by one type of scale, usually a hard-shelled creature that looks like a miniature turtle shell. Adult scale, while true insects, tend to be sessile, which is a fancy entomological word meaning they don’t move. You’d be hard-pressed to find the legs on the creature, if you could turn them over without killing them.

While there tends to be one type of scale on magnolia, it can take on a couple different forms. Left unchecked, it’s possible this creature can do serious damage to limbs and branches. Death of the tree is possible.

As the female scale develops, she forms white, waxy hairs around the shell, which can give the illusion that there’s popcorn on the branches.

What’s really obvious is the sooty mold growing on the sappy excretion from the scale. Leaves take on this black appearance, which can be rubbed off. The sooty mold isn’t harmful per se, though it does cut down on the tree’s ability to produce sugars.

Soon, the females and males will get together, eggs will be laid, and then crawlers will emerge from the eggs. This occurs between now and October.

Once the crawlers are moving, they are prime targets for predatory insects or insecticides. However, most insecticides won’t work on the waxy adults.

If you have scales on your magnolia, you can spray them with highly refined summer horticulture oil. This oil suffocates the scales without harming the tree. Not all oils work, so you have to find the summer types.

Come November through March, you could spray the trees with dormant oil, which won’t damage anything but the insects. Of course, there are no leaves during this time to damage.

There are several insecticides on the market that will control the crawlers. Read and follow the directions on the label. Do not mix the product stronger than what’s listed.

And if you can get a bunch of ladybugs to descend on the branches, you have another control option.

David Robson is a horticulture educator for the University of Illinois Extension.

Never miss a story

Choose the plan that's right for you.
Digital access or digital and print delivery.